Design advice should be the beginning of the die casting process
Pacific Die Casting should be consulted in the beginning stage in order that a proposed design, or existing part, can be evaluated early for die casting, and the design optimized for lowest-cost die cast production.
Die casting is one of the fastest and most cost-effective methods for producing a wide range of components. However, to achieve maximum benefits from this process, it is critical that designers collaborate with the die caster at an early stage of the product design and development. Consulting with the die caster during the design phase will help resolve issues affecting tooling and production, while identifying the various trade-offs that could affect overall costs.
For instance, parts having external undercuts or projections on sidewalls often require dies with slides. Slides increase the cost of the tooling, but may result in reduced metal use, uniform casting wall thickness or other advantages. These savings may offset the cost of tooling, depending upon the production quantities, and provide overall economies.
Many sources are available for information on die casting design, including textbooks, technical papers, trade journals and professional associations. While this section is not intended to provide a comprehensive review of all the factors involving die casting design, it will highlight some of the primary considerations. One of the first steps in designing a die cast component is choosing the proper alloy.
Effective Design
A number of factors affect the final design of a die cast component. Often, however, simple design changes can have a significant impact on the cost, speed of production and usefulness of the part. For example, casting drill spots may be preferred to casting a cored through hole. Even though an extra step is required, offhand drilling after casting may be simpler and less expensive than creating a complex die with numerous cores.
CAD and Cast-Flow Simulation
With all customer prints or computer files at hand for CAD die design, Pacific Die Casting can often make important castability suggestions for significant cost reductions-or eliminate future casting problems which later processing adjustments may be unable to overcome.
Pacific Die Castingís use of cast-flow simulation and thermal analysis software, prior to die construction, optimizes die gating and runner designs to assure proper metal flow and fill.
We Are Here To Help You From The First Step
The basic die casting process consists of injecting molten metal under high pressure (forces exceeding 4500 pounds per square inch) into a steel mold called a die. Die casting machines are typically rated in clamping tons equal to the amount of pressure they can exert on the die. Machine sizes range from 20 tons to 4000 tons. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. The two methods are hot chamber and cold chamber. (Hot chamber machines immerse the metal injection mechanism in molten metal and cold chamber machines do not.) .A complete die casting cycle can vary from less than one second for small components weighing less than an ounce, to two-to-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts.
Die Casting vs. Plastic Molding
Die casting produces stronger parts with closer tolerances that have greater stability and durability. Die cast parts have greater resistance to temperature extremes and superior electrical properties.
Compared with the most widely specified plastic injection moldings, die castings are stronger, stiffer, more stable dimensionally, more heat resistant, and are superior to plastics based on mechanical properties per unit of cost. Die castings have a high degree of permanence under load when compared to plastics and are far more resistant to ultra-violet irradiation, weathering and stress cracking in the presence of various reagents. Castings offer built-in EMI/RFI shielding, which is often a problematic and costly post-casting operation with plastic housings.
Die Casting vs. Sand Casting
Die casting produces parts with thinner walls, closer dimensional limits and smoother surfaces. Compared with sand castings, die castings require little or no machining to meet specifications, can be made with thinner walls, can have all or nearly all holes cored to size, can be held within much closer dimensional limits, and are produced more rapidly in dies which can make many thousands of castings without replacement, rather than requiring new cores for each casting. Production is faster and labor costs per casting are lower. Finishing costs are also less. Sand castings require a new sand mold with each casting or gate of castings.
At what quantity does conversion to a die casting from a sand casting, or other gravity casting process make economic sense? The answer depends largely on the configuration, size and complexity of the part. While the die casting process is most economic at higher volumes, die casting can achieve comparative savings at quantities at or below 2,000 pieces if extensive post-casting machining or surface finishing can be eliminated
Die Casting vs. Permanent Mold
Die casting offers the same advantages versus permanent molding as it does compared with sand casting. The permanent mold gravity process uses iron or steel molds, but, like the sand process, is far slower and less precise than die casting. Die castings can be made to closer dimensional limits and with thinner sections than permanent mold castings. Holes can be cored in die castings, and they are produced at higher rates with less manual labor. They have smoother surfaces and usually cost less per part.
Die Casting vs. Forging
Die casting produces more complex shapes with closer tolerances, thinner walls and lower finishing costs. Cast coring holes are not available with forging.
Where a die casting alloy can satisfy the design requirements for strength and density, die casting will offer complex shapes not possible in forged parts, with thinner sections held to closer tolerances. A new generation of metal matrix composites, squeeze cast, and semi-solid cast parts are offering significant cost savings over forgings at substantial weight reductions.
Die Casting vs. Stamping
Die casting produces complex shapes with variations possible in section thickness. One casting may replace several stampings, resulting in reduced assembly time.
When a highly complex stamping or several stampings are required, die casting can be a cost-effective alternative, and can achieve complex shapes impossible with a stamping. In the case of multiple stampings, costs of fixturing and welding added to the costs of fabricating the additional parts can make die casting very competitive. Material costs for stamping may be substantially higher than indicated by published per pound costs due to high scrap rates. Stampings invariably consume more material than is contained in the end product, sometimes substantially more.
Die Casting vs. Screw Machine Products
Die casting produces shapes that are difficult or impossible to create from bar or tubular stock, while maintaining tolerances without tooling adjustments. Die casting requires fewer operations and reduces waste and scrap.
The automatic screw process uses bar stock as raw material which offers very poor material utilization ó sometimes less than 50%. This choice will usually depend on production quantities, with the die casting advantage increasing as production rates increase. Unusually complex design shapes are routinely produced as die castings, while they would be costly or impossible as machined parts.
The Future of Die Casting
Die casting is one of the great processes of the future. Few other processes add as much value to raw material in such a short time, or as cost effectively.
The high technology applications of U.S. die castings helps to assume continued steady growth of the process in manufacturing.
The increased use of lighter-weight metal components, such as aluminum die castings, has spurred growth in the automotive sector. Today, there is an average of 220 lb. of aluminum castings per vehicle, an amount projected to grow to 300 lb. per year by the year 2006.
At the federal level, die casters maintain that the largest government challenge they face is environmental regulation. The paperwork associated with environmental regulation is a primary concern. The constant effort required to keep up with new rules is particularly problematic for smaller die casters with limited resources and finances.
Regulatory reforms are needed to promote a healthy long-term climate for economic growth.
The automation of equipment, new processes, and the stringent requirements for casting to perform even more difficult tasks pose a great opportunity and challenge to the die casting industry for the future.
When Is It Best To Use Die Casting?
The cost of materials is another important design consideration. Accurate comparisons require looking beyond the cost per pound or cost per cubic inch to fully analyze the advantages and disadvantages of each competing process. For instance, the relatively greater strength of metals generally allows thinner walls and sections and consequently requires fewer cubic inches of material than plastics for a given application.
The Proper Alloy
Each of the metal alloys available for die casting offer particular advantages for the completed part.
Zinc
The easiest alloy to cast, it offers high ductability, high impact strength and is easy to plate. Zinc is economical for small parts, has a low melting point and promotes long die life.
Thinner sections and smaller parts can be die cast in zinc than in other commonly used die casting alloys. Zinc alloy generally allows for greater variation in section design and for the maintenance of closer dimensional tolerances. Zinc alloy produces the best chrome plating results. The impact strength of zinc components is higher than other die casting alloys, with the exception of brass. Due to the lower pressures and temperatures required for zinc, die life is significantly lengthened and die maintenance is minimized. Zamak No. 3 offers the best combination of mechanical properties, castability and economics and is the most widely used Zn alloy in North America.
Aluminum
This alloy is lightweight, while possessing high dimensional stability for complex shapes and thin walls. Aluminum has good corrosion resistance and mechanical properties, high thermal and electrical conductivity, as well as strength at high temperatures.
Aluminum die casting alloys have a specific gravity of approximately 2.7 g/cc, placing them among the lightweight structural metals. The majority of die castings produced worldwide are made from aluminum alloys, with good corrosion resistance and good mechanical properties. Aluminum die castings offer high dimensional stability, thermal and electrical conductivity, and strength at high temperatures. Aluminum 380 alloy is the most widely used of the Al die casting alloys, offering the best combination of properties and ease of production.
Magnesium
The easiest alloy to machine, magnesium has an excellent strength-to-weight ratio and is the lightest alloy commonly die cast.
Copper
This alloy possesses high hardness, high corrosion resistance and the highest mechanical properties of alloys cast. It offers excellent wear resistance and dimensional stability, with strength approaching that of steel parts.
Lead and Tin
These alloys offer high density and are capable of producing parts with extremely close dimensions. They are also used for special forms of corrosion resistance.
Choosing
Glossary Of Die Casting Industry Terms:
Automation Industry term commonly used to describe the mechanization of various aspects of the die casting process.
Biscuit
Excess of ladled metal remaining in the shot sleeve of a cold chamber die casting machine. It is part of the cast shot and is removed from the die with the casting.
Blister
A surface bubble caused by gas expansion (usually from heating) which was trapped within the die casting or beneath the plating.
Blow holes
Voids or pores which may occur due to entrapped gas or shrinkage during solidification, usually evident in heavy sections (see porosity).
Cavity
The recess or impressions in a die in which the casting is formed.
Cold chamber machine
A type of casting machine in which the metal injection mechanism is not submerged in molten metal.
Checking
Fine cracks on the surface of a die which produce corresponding raised veins on die castings. Caused by repeated heating of the die surface by injected molten alloys.
Creep
Plastic deformation of metals held for long periods at stresses lower than yield strength.
Die lubricant
Liquid formulations applied to the die to facilitate casting release and prevent soldering.
Dimensional stability
Ability of a component to retain its shape and size over a long period in service.
Dowel pin
A guide pin which assures registry between cavities in two die halves.
Draft
The taper given to walls, cores and other parts of the die cavity to permit easy ejection of the casting.
Ejector marks
Marks left on castings by ejector pins.
Ejector plate
A plate to which ejector pins are attached and which actuates them.
Fillet
Curved junction of two surfaces, e.g., walls which would meet at a sharp angle.
Flash
A thin web or fin of metal on a casting which occurs at die partings, vents and around moveable cores. This excess metal is due to working and operating clearances in a die.
Gate
Passage for molten metal which connects runner with die cavity. Also, the entire ejected content of a die, including castings, gates, runners, sprue (or biscuit) and flash.
Gooseneck
Spout connecting a metal pot or chamber with a nozzle or sprue hole in the die and containing a passage through which molten metal is forced on its way to the die. It is the metal injection mechanism in a hot chamber die casting machine.
Growth
Expansion of a casting as a result of aging or of intergranular corrosion, or both.
Heat checking
(See checking)
Hot chamber machines
Die casting machines which have the plunger and gooseneck (metal pressure chamber) immersed in molten metal in the holding furnace.
Hot short
Term used to describe an alloy which is brittle or lacks strength at elevated temperatures.
Impact strength
Ability to resist shock, as measured by a suitable testing machine.
Impression
Cavity in a die. Also, the mark or recess left by a ball, or penetrator of a hardness tester.
Ingot
Metal or alloy cast in a convenient shape for storage, shipping and remelting.
Injection
The process of forcing molten metal into a die.
Insert
A piece of material, usually metal, which is placed in a die before each shot. When molten metal is cast around it, it becomes an integral part of the die casting.
Intergranular corrosion
A type of corrosion which preferentially attacks grain boundaries of metals or alloys, resulting in deep penetration.
Loose piece, knockout
A type of core (which forms undercuts) which is positioned in, but not fastened to a die. It is arranged so as to be ejected with the casting, from which it is removed. It is used repeatedly for the same purpose.
Metal saver
Core used primarily to reduce amount of metal in a casting and to avoid sections of excessive thickness.
Multiple cavity die
A die having more than one duplicate impression.
Nozzle
Outlet end of a gooseneck or the tubular fitting which joins the gooseneck to the sprue hole.
Overflow-well
A recess in a die connected to a die cavity by a gate to assist in proper venting.
Parting line
A mark left on a die casting where the die halves meet; also, the mating surface of the cover and ejector portions of the die.
Plunger
Ram or piston which forces molten metal into a die.
Port
Opening through which molten metal enters the injection cylinder.
Porosity
Voids or pores resulting from trapped gas or shrinkage during solidification.
Process control
Where parameters of a process are studied and correctly applied in the manufacturing process to produce high quality parts.
Runner
Die passage connecting sprue or plunger holes of a die to the gate where molten metal enters the cavity or cavities.
Shot
That segment of the casting cycle in which molten metal is forced into the die.
Shrinkage, solidification
Dimensional reduction that accompanies the freezing (solidification) of metal passing from the molten to the solid state.
Shrink mark
A surface depression which sometimes occurs next to a heavy section that cools more slowly than adjacent areas.
Slide
The portion of the die arranged to move parallel to die parting. The inner end forms a part of the die cavity wall that involves one or more undercuts and sometimes includes a core or cores.
Soldering
Adherence of molten metal to portions of the die.
Split gate
A gate of castings having the sprue or plunger axis in the die parting.
Sprue
Metal that fills the conical passage (sprue hole) which connects the nozzle with runners.
Sprue pin
A tapered pin with rounded end projecting into a sprue hole and acting as a core which deflects metal and aids in the removal of the sprue.
Toggle
Linkage employed to mechanically multiply pressure when locking the dies of a casting machine.
Trim die
A die for shearing or shaving flash from a die casting.
Unit die
A die interchangeable with others in a common holder.
Undercut
Recess in the side wall or cored hole of a casting disposed so that a slide or special form of core (such as a knockout) is required to permit ejection of the casting from the die.
Vent
Narrow passage at the die parting which permits air to escape from the die cavity as it is filled with molten metal.
Void
A large pore or hole within the wall of a casting usually caused by entrapped gas. A blow hole.
Waterline
A tube or passage through which water is circulated to cool a casting die.